As methods for smelting nickel oxide ore called limonite or saprolite, a method of dry smelting that produces nickel matt using a flash smelting furnace, a method of dry smelting that produces ferronickel using a rotary kiln or moving hearth furnace, a method of wet smelting that produces a mix sulfide using an autoclave, etc. have been known.
Upon charging the nickel oxide ore to the smelting step, pre-processing is performed for pelletizing, making into a slurry, etc. the raw material ore. More specifically, upon pelletizing the nickel oxide ore, i.e. producing pellets, it is common to mix components other than this nickel oxide ore, e.g., binder and reducing agent, then further perform moisture adjustment, etc., followed by charging into agglomerate producing equipment to make a lump on the order of 10 to 30 mm, for example (indicated as pellet, briquette, etc.; hereinafter referred to simply as “pellet”).
It is important for this pellet to maintain the shape thereof even if the smelting operations such as loading into a smelting furnace and reducing and heating is begun in order to achieve the roles such as preserving breathability and prevention of uneven distribution of raw material components, for example.
For example, Patent Document 1 discloses technology of adjusting excess carbon content of the mixture in a mixing step to make a mixture by mixing raw materials including nickel oxide and iron oxide with carbonaceous reducing agent, as a pre-treatment method upon producing ferronickel using a moving hearth furnace.
However, when pelletizing this mixture in order to load into the smelting furnace, and heating to the reduction temperature, so-called heat-shock may occur whereby the pellets break, and there are problems of inhibiting progression of the smelting reaction, or the product becoming smaller and recovery becoming difficult. Therefore, commercial operation becomes difficult if not curbing at least the proportion of pellets broken by heat shock to on the order of 10%.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2004-156140